Non-pharmacological Management of Non-productive Chronic Cough in Adults: A Systematic Review.

Only five studies met the criteria, and they differed too much in their populations, treatments and outcome measures for the results to be pooled. Every reported finding therefore rests on one or two small trials rather than a combined estimate. Samples were small, ranging from 9 to 43 per group, effects were small and confidence intervals were wide. The authors state this limits confidence in establishing the impact of these therapies. Five of the six articles were rated as having some concerns for risk of bias and one as high risk, mainly because none registered their outcomes and planned analyses in advance, so it is not clear whether reported outcomes were chosen after the results were known. Interventions lasted only one to eight weeks, and the authors acknowledge that a one-week intervention is unlikely to change a cough that has lasted several years. Long-term effects of these therapies are unknown. Everyone in the included studies had a dry cough with normal chest imaging and few or no other respiratory problems, so these results say nothing about patients with significant lung disease or those who produce sputum. Dropouts were substantial in some studies, up to 35%, which may bias the results in either direction. Only studies published in English, Portuguese or French were included, and complementary therapies such as acupuncture were excluded, so some non-drug approaches are not represented. Results for people with refractory cough and asthma were not reported separately, so nothing can be concluded about asthma specifically.

The authors declare no commercial or financial relationships that could be seen as a conflict of interest. The review itself reports no industry funding; two authors hold research chairs, one from the National Sanitarium Association in Respiratory/Pulmonary Rehabilitation Research and one from the Canada Research Chairs programme in Critical Care Rehabilitation and Knowledge Translation. In one of the included trials, not in this review itself, the CPAP equipment was provided by Philips-Respironics.

Do not read the improvements in cough-related quality of life and voice as proof that these therapies work. Only five small trials were included, the studies were too different to combine, most had concerns for risk of bias, and the authors themselves conclude the evidence is insufficient for clinical recommendations.